[dm-devel] [RFC PATCH 1/2] percpu_ref: add percpu_ref_tryget_many_live

[Ming Lei]

Prepare for support freezing bio based request queues.

Cc: Tejun Heo <tj at kernel.org>
Cc: Christoph Hellwig <hch at lst.de>
Cc: Bart Van Assche <bvanassche at acm.org>
Signed-off-by: Ming Lei <ming.lei at redhat.com>
---
 include/linux/percpu-refcount.h | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/include/linux/percpu-refcount.h b/include/linux/percpu-refcount.h
index 16c35a728b4c..9061c7e3113d 100644
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -267,8 +267,9 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
 }
 
 /**
- * percpu_ref_tryget_live - try to increment a live percpu refcount
+ * percpu_ref_tryget_many_live - try to increment a live percpu refcount
  * @ref: percpu_ref to try-get
+ * @nr: number of references to get
  *
  * Increment a percpu refcount unless it has already been killed.  Returns
  * %true on success; %false on failure.
@@ -281,7 +282,8 @@ static inline bool percpu_ref_tryget(struct percpu_ref *ref)
  *
  * This function is safe to call as long as @ref is between init and exit.
  */
-static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
+static inline bool percpu_ref_tryget_many_live(struct percpu_ref *ref,
+					       unsigned long nr)
 {
 	unsigned long __percpu *percpu_count;
 	bool ret = false;
@@ -289,10 +291,10 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
 	rcu_read_lock();
 
 	if (__ref_is_percpu(ref, &percpu_count)) {
-		this_cpu_inc(*percpu_count);
+		this_cpu_add(*percpu_count, nr);
 		ret = true;
 	} else if (!(ref->percpu_count_ptr & __PERCPU_REF_DEAD)) {
-		ret = atomic_long_inc_not_zero(&ref->data->count);
+		ret = atomic_long_add_unless(&ref->data->count, nr, 0);
 	}
 
 	rcu_read_unlock();
@@ -300,6 +302,26 @@ static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
 	return ret;
 }
 
+/**
+ * percpu_ref_tryget_live - try to increment a live percpu refcount
+ * @ref: percpu_ref to try-get
+ *
+ * Increment a percpu refcount unless it has already been killed.  Returns
+ * %true on success; %false on failure.
+ *
+ * Completion of percpu_ref_kill() in itself doesn't guarantee that this
+ * function will fail.  For such guarantee, percpu_ref_kill_and_confirm()
+ * should be used.  After the confirm_kill callback is invoked, it's
+ * guaranteed that no new reference will be given out by
+ * percpu_ref_tryget_live().
+ *
+ * This function is safe to call as long as @ref is between init and exit.
+ */
+static inline bool percpu_ref_tryget_live(struct percpu_ref *ref)
+{
+	return percpu_ref_tryget_many_live(ref, 1);
+}
+
 /**
  * percpu_ref_put_many - decrement a percpu refcount
  * @ref: percpu_ref to put
-- 
2.29.2